The objectives of the proposed research are to investigate the cellular and humoral components of the host defense mechanisms against group B streptococci. Studies will be carried out to determine the effect of types specific antibodies and components of the complement system on opsonization of the five types of group B organisms. In addition, bacterial factors important in virulence will be investigated. These will include soluable factors that might alter cellular functions such as chemotaxis or bactericidal activity, and structural components such as fimbrae which might impede phagocytosis. In addition, host defense parameters including specific antibodies, complement activity, and the neutrophil functions chemotaxis, random migration, phagocytosis, and bactericidal activity will be determined in infected, colonized, and uncolonized neonates and adults. The proposed research will also include the continued evaluation of a counterimmunoelectrophoresis procedure developed in our laboratory for the rapid detection of group B streptococci. Should abnormalities of the cellular or humoral components of the host defense mechanism be detected in patients with group B infections, attempt will be made to correct such abnormalities using passively administered antibody or complement, active immunization, or individual blood components (i.e. leukocytes). Correction would be attempted in vitro, in an experimental animal model of group B sepsis, and lastly, in patients with group B streptococcal infections.